如何注释一个由多个鸭子类型组合而成的类型？

Question

Let's say I want to annotate the parameter to a function, and it should satisfy both typing.Sized and typing.Hashable (any other 2+ types could apply, I just picked these two for the sake of example). How would I annotate this?

Given that one can combine types as an "or" using Sized | Hashable Sized | Hashable , I would expect something like: Sized & Hashable or Sized + Hashable to work, but unfortunately it doesn't (at the time of writing on Python 3.10).

Is this supported at all, and if so with what syntax?

Answer 1

Sized & Hashable is a reasonable guess, but unfortunately intersection types are not supported.

You'll have to define your own subclass that inherits from both:

class SizedHashable(Sized, Hashable):
    pass

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There seems to be some effort being made to support intersection types, but I can't find any updates beyond this brief mention.